1. Field of the Invention
The present invention relates to a wireless communications system, especially to a wireless communications system for bit-error-free packet transmission. The invention also relates to a method for such wireless communications.
2. Description of the Background Art
Since the packet transmission carried out between digital devices such as computers, etc., in the form of units of bit streams does not permit any bit error to occur, bit-error-free packet transmission is generally employed.
In the packet transmission, bit-error-free transmission is realized by means of a communication protocol named handshaking. The handshaking proceeds in the following manner. A data transmitter, or sender, adds an error detection code to packet data, and then sends out the packet data. A data receiver uses the error detection code to detect any bit error in the received packet data. When the data receiver detects no error in the packet data, it sends out a response signal named ACK (ACKnowledgement) packet. When the data receiver detects any error, it cancels the received packet data and waits. When the data sender receives the response signal from the data receiver within a preset period of time, the data sender will proceed to resending the packet data in question.
As a system to implement bit-error-free packet transmission, Japanese patent laid-open publication No. 2002-26984 discloses a communications system in which, in order to reduce the error rate in ACK packets, the data field of an ACK packet is used for the indication of a response signal to reduce the number of bits required for the ACK packet and the ACK packet is sent out in the form of including an error detection code.
In a communications system disclosed in above-mentioned patent document, however, there is a problem that, if a data receiver received packet data without any bit error and sent out an ACK packet to a data sender, and thereafter the data sender detects error in the received ACK packet based on its error detection code included in the ACK packet, then the data sender fails to confirm the ACK packet, and consequently determines that it has received no ACK packet within a preset period of time to resend out the packet data in question, as would be unnecessary, thus deteriorating transmission efficiency.